Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises a housing in which is provided an exhaust gas driven turbine wheel mounted on a rotatable shaft connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft. The compressor wheel delivers compressed air to the engine intake manifold. Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that the size of the turbine inlet passage can be varied to optimize gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suit varying engine demands.
As a result of the operating conditions to which conventional turbine wheels are exposed during use they can fail due to fatigue. It would therefore be desirable to improve the fatigue resistance or fatigue durability of turbine wheels.